A force sensor is mounted on a wrist portion of a robot arm, for example, in assembling parts with the robot arm, and is used to detect a force/moment component generated during the assembly work and perform posture control of a hand portion of the arm. A conventional typical force sensor makes detection from a resistance change in a strain gauge, as disclosed in Japanese Patent Application Laid-Open No. H01-262431. In addition, there is also another force sensor using a method of magnetically detecting a displacement of an action portion, as disclosed in Japanese Patent Application Laid-Open No. 2004-325328.
First, FIG. 11 illustrates a conventional structural example described in Japanese Patent Application Laid-Open No. H01-262431. A force/moment component working on a strained portion is calculated from a resistance change in a plurality of strain gauges arranged on an identical beam.
Next, FIGS. 12A and 12B illustrate a conventional structural example disclosed in Japanese Patent Application Laid-Open No. 2004-325328, respectively. There are disposed a permanent magnet embedded into an elastic body and four magnetoelectric transducers (Hall elements) provided so as to face a magnetization direction axis (S-N axis) of the permanent magnet. When an action force is applied, the permanent magnet displaces and a change in magnetic flux caused by the displacement is converted into an electric signal for detection by the magnetoelectric transducer. This enables detection of three shaft force components in X-axis, Y-axis and Z-axis directions.
However, an invention of Japanese Patent Application Laid-Open No. H01-262431 is arranged with a plurality of strain gauges on an identical beam. Accordingly, when a strained portion receives a force, there occurs a problem of interference between axes when an axial strain occurs, not only in a direction in which an applied force works but also in one in which no force works. In addition, reducing the shaft interference requires one to devise a beam structure and signal processing, which are disadvantageous in terms of a desire to achieve size and cost reductions. Further, because a strain gauge uses a strain generated when a force is applied, repeated use will cause a problem with durability and reliability due to secular changes.
On the other hand, an invention of Japanese Patent Application Laid-Open No. 2004-325328 has such a structure that elements provided in no contacts are independent, respectively, which compensates for demerits of the invention of Japanese Patent Application Laid-Open No. H01-262431.
However, such a structure that a magnetic material faces a magnetoelectric transducer scatters magnetic flux and therefore, a displacement of magnetic flux density detected by the magnetoelectric transducer occurs only a little, which makes it difficult to obtain high sensitivity. Further, the magnetic material is embedded simply with an elastic body, which causes problems such as generation of a noise source having an adverse effect on peripheral apparatuses and external magnetic flux easily flowing into the magnetoelectric transducer having an adverse effect on output.
In view of the foregoing problems, it is an object of the present invention to provide a magnetic force sensor which detects force/moment in 6-axis directions using such a structure as to restrain an adverse effect of a magnetic flux generation source onto the outside and to improve reliability against noise and high sensitivity.